CASE REPORTSVenous thromboembolism associated with hyperhomocysteinemia, homozygosity for the methylenetetrahydrofolate reductase 677C>T gene variant, and secondary polycythemiaMasuda, Kazunoria; Imashuku, ShinsakubAuthor Information aDepartment of Cardiovascular Medicine bDepartment of Laboratory Medicine, Uji-Tokushukai Medical Center, Uji, Kyoto, Japan Correspondence to Shinsaku Imashuku, MD, PhD, Department of Laboratory Medicine, Uji-Tokushukai Medical Center, Uji 611-0041, Kyoto, Japan Tel: +81 774 20 1111; fax: +81 774 20 2336; e-mail: email@example.com Received 23 April, 2019 Revised 25 December, 2019 Accepted 13 January, 2020 Blood Coagulation & Fibrinolysis: June 2020 - Volume 31 - Issue 4 - p 270-273 doi: 10.1097/MBC.0000000000000897 Buy Metrics Abstract The development of pulmonary embolism/deep vein thrombosis (DVT) in the extremities is influenced by various risk factors. Hyperhomocysteinemia is one such risk factor, which may be associated with vitamin B12/folate deficiency, or the methylenetetrahydrofolate reductase gene variant, 677C>T. Here, we report a 47-year-old male who developed pulmonary embolism/DVT, associated with hyperhomocysteinemia (plasma homocysteine: 71.9 nmol/ml; reference range: 6.3–18.9 nmol/ml) and was homozygous (T/T) for the methylenetetrahydrofolate reductase variant. Serum levels of vitamin B12 and folate were within the normal range, while secondary polycythemia (hemoglobin: 18.2 g/dl and hematocrit: 50.8%) may have acted as an additional trigger for the thromboembolism. The pulmonary embolism/DVT was successfully managed and the patient has been doing well for longer than 3 years. Copyright © 2020 YEAR Wolters Kluwer Health, Inc. All rights reserved.